1. Field of the Invention
The present invention relates to an optical communication network, and more particularly to a passive optical network.
2. Description of the Related Art
A wavelength division multiplexing passive optical network (hereinafter, referred to as a WDM-PON) provides an ultra high-speed broadband communication service using specific wavelengths assigned to each subscriber unit. Therefore, a WDM-PON can ensure the secrecy of communication between subscriber units, can accommodate special communication services required from each subscriber unit, easily expand the channel capacity, and can easily increase the number of subscriber units by adding specific wavelengths to be assigned to new subscribers. Generally, a WDM-PON uses a double star structure in order to minimize the length of optical line. That is, a central office (CO) and a remote node (RN) installed at an area adjacent to optical network units (ONUs) are connected to each other through one feeder optical fiber. The remote node and each optical network unit are connected to each other through a separate distribution optical fiber. Multiplexed downstream optical signals are transmitted to the remote nodes through the feeder fiber and, the multiplexed downstream optical signals are de-multiplexed by a wavelength division multiplexer installed in the remote node. The de-multiplexed signals are transmitted to the optical network units through the distribution fibers. Similarly, upstream optical signals are outputted from the optical network units and transmitted to the remote node. The upstream optical signal are multiplexed by the wavelength division multiplexer and the multiplexed signal is transmitted to the central office.
In the WDM-PON, large amounts of data are transmitted at high speed through the wavelengths assigned to corresponding optical network units. Accordingly, when an unexpected abnormality (such as a malfunction or deterioration) of an upstream light source or a downstream light source, or an abnormality (such as a cut or deterioration) of a feeder fiber or distribution fiber occur, the transmitted data may be lost even if the abnormality occurs for a short time. Accordingly, such an abnormality must be quickly detected and instantly healed.
Recently, research into a wavelength injection light source, such as a wavelength locked Fabry-Perot laser and reflective semiconductor light source, capable of outputting an optical signal having the same wavelength as that of light injected to a light source for a WDM PON and performing a direct modulation has been pursued.
Hence, it is necessary to develop a WDM self-healing PON capable of quickly detecting an abnormality in feeder or distribution fibers and also healing the abnormality by itself.